Synthetic gemstones made of lead-free and lead-containing glass and synthetic precious stones are usually fabricated in completely different qualities. In many countries, gemstones are subject to so-called product compliance guidelines, which limit the content of possibly harmful components.
On the gemstone sector, there has been a strong competition with a massive price pressure in the world market since about 2005. Brand products are often copied, or traded under false statements of origin. Because of the enormous variety of the traded stones, a quick distinction between original and copy is very difficult. The damage caused by trademark counterfeiting is enormous. In addition, the gemstone copies often do not meet the same quality standards and compliance regulations; depending on the country, harmful components may lead to enormous liability problems.
At present, it is common to check the authenticity of synthetic gemstones in accordingly specialized laboratories. For this purpose, the chemical composition of the glass of the gemstone is determined, and its grinding geometry/brilliance is analyzed and compared. Such tests are relatively expensive and time-consuming and cannot be employed for a quick analysis on the market.
A known method for identifying synthetic gemstones is labeling with laser engraving. Because of its high cost and technical limits, this method can be employed for synthetic gemstones of glass only to a very limited extent.
In order to protect luxury products from trademark counterfeiting, numerous product authentication solutions exist, such as multistage safety stickers, holograms, safety inks, RFID (radio frequency identification) systems, etc. However, these methods are not applicable to gemstones, because they would adversely affect the optical appearance of the gemstone.
A combination of luminescent markers that can be applied to or introduced in articles is known from WO 2011/141461 A1 (Uni Berlin). These luminescent markers cannot be molten into the glass with preservation of the chemical bonds. Rather, the original chemical compounds that were the components of the luminescent markers are dissolved in the glass network after the melting. The original luminescence of the ceramic particles according to the patent is lost and therefore can no longer be detected in the finished products.
Luminescent phosphorous glasses that contain more than 2 mole percent of particular oxides of rare earth metals are known from patent specification US 2005 0253113 (Schott). Quartz glasses doped with rare earth elements are known from EP 0 466 932 A1 (Furukawa).
Glass beads containing dopants selected from rare earths in amounts of 0.5 to 3 mole percent are known from U.S. Pat. No. 7,256,398. However, dopants are undesirable in glass in such relatively high concentrations, because rare earths are known to change the color of the glass. In addition, dopants added in the above mentioned concentrations lead to significant increases of the raw material cost of the glass mixture, so that such compositions can no longer be employed in an economically efficient way for synthetic gemstones.
Dopants in concentrations of one-digit percentages (1% corresponds to 10,000 mg/kg) can be detected relatively simply with common analytical methods, such as RFA. However, they lead to colorings of the glasses and therefore are not suitable as dopants in such concentrations.
It is the object of the present invention to provide faceted gemstones of glass that are luminescent, but contain so small amounts of dopants that they do not cause color changes in the glass on the one hand, but have clearly identifiable bands in the emission spectrum on the other. The dopants serve as “markers of authenticity” and enable identification through a portable analytical device.